1. Technical Field
The present invention relates generally to wireless communications, and, specifically, to an antenna system that includes a plurality of antenna elements, each of which is phase shifted so that the antenna system provides a relatively wide bandwidth of operation. The present invention further relates to an antenna system having phase shifting circuitry that produces an apparent short circuit to connected radio circuitry at harmonic frequencies of a frequency design range.
2. Related Art
It is well known to couple an antenna to radio circuitry contained within a host unit to enable wireless communication between the host unit and remotely located units. Typical implementations of such technology include cellular systems wherein portable terminals wirelessly communicate voice and data information to and from central locations via a wireless link.
A particular problem in the design of portable terminals operating in such systems relates to the antennas employed. Such antennas must perform adequately within a frequency design range while not interfering with space considerations and other physical aspects of the portable terminal. Antennas that protrude from the portable terminal perform well, but cause problems where the terminal must be able to dock into another device, and tend to be susceptible to breakage in rugged environments. Antennas that conform to the outer perimeter of the portable terminal do not interfere with physical aspects of the portable terminal, but their characteristics at harmonic frequencies do not always conform to FCC power level requirements, such requirements limiting permissible emissions at harmonic frequencies of the frequency design range.
In many applications, such as with spread-spectrum radio technology that has become popular in portable radio terminal communications, antennas must be designed to operate over a relatively large bandwidth. As the physical size of antennas decreases, however, so does respective bandwidth and gain. Prior, non-protruding antennas provided insufficient bandwidth and gain in spread-spectrum applications. Thus, heretofore, protruding antennas have proven the solution of choice in spread-spectrum applications even though they are often damaged during use.
Thus, there lies a need for an improved internal antenna design that provides adequate performance, operates adequately over a large bandwidth, conforms to FCC harmonic power level requirements, and yet is reasonably inexpensive to implement in portable terminals.